1. Field of the Invention
The present invention generally relates to a system and method for determining dynamic traffic information. More particularly, the present invention relates to generating dynamic traffic information based on locational measurements.
2. Description of the Related Art
Two kinds of traffic information have traditionally been gathered: qualitative data and quantitative data. Qualitative data is typically gathered through reports from traffic helicopters or traveler call-ins. Quantitative data is usually gathered by public agencies, such as state departments of transportation, via fixed installation surveillance systems. The most common fixed installation surveillance systems use inductive loops embedded in roadways. These systems can be expensive to install and can require expensive, on-going maintenance.
Other kinds of surveillance systems that use radar guns, microwaves, video surveillance, or electronic toll tags have been proposed or are in development. All of these surveillance systems typically have high installation costs because they require equipment to be installed along the roads. Additionally, these surveillance systems typically have high operating costs due to ongoing maintenance costs and the cost of bandwidth needed to transmit signals from the surveillance systems to a central office. Furthermore, these surveillance systems typically require installation on public property, which limits the ability of private companies to install and operate such surveillance systems. Because surveillance systems are typically expensive to install and operate, use of these systems is typically limited to freeway or highway surveillance only.
One alternative to fixed installation surveillance systems uses probes, such as electronic devices, to gather quantitative data about the vehicles in which the probes are located. However, such probe systems have traditionally faced two primary limitations. The first limitation is a lack of sufficient numbers of probes from which to gather information. In particular, insufficient numbers of probes limits the ability of a system to generate information for large numbers of streets. The second limitation is the difficulty of determining the particular roads on which the probe travels. More particularly, the difficulty of placing a vehicle on a particular road can limit the accuracy of the information gathered about the vehicle.
The recent development of location systems for determining the position of a cellular phone or other electronic device addresses the first limitation and allows for the development of a probe system with much greater capabilities than previously possible. In particular, tracking the increasing number of cell phones can overcome the first limitation of insufficient numbers of probes. By tracking cell phones, a probe system can track thousands of probes simultaneously over a local road network.
However, with the current location systems available, the second limitation, the difficulty of determining the particular roads on which the probe travels, is a major problem. Current systems typically can only locate a phone within a radius of about 50 meters to about 300 meters, depending on the technology used, atmospheric conditions, and the specific location of the phone. Accordingly, locating a phone using current systems presents a serious challenge for a probe system because a radius of about 300 meters can include a very large number of roads. Furthermore, present approaches to probe systems generally depend on knowing the location of the vehicle to within about 5 meters to about 10 meters.